1. Field of the Invention
The present invention relates to a semiconductor memory device. In particular, the present invention relates to the semiconductor memory device including a memory cell having a recording layer whose resistance value changes and which records data.
2. Description of the Related Art
There has been known a magnetic memory device as one of a semiconductor memory device. Various types of magnetic memory devices have been conventionally proposed. Recently, a magnetic random access memory (MRAM) using a magnetoresistive element having giant magnetoresistive (GMR) effect has been proposed. A magnetic random access memory using ferromagnetic tunnel junction has attracted special interest.
For example, the ferromagnetic tunnel junction is composed of three layers, that is, first ferromagnetic layer, insulating layer and second ferromagnetic layer, and current flows using the insulating layer as a tunnel. In this case, the junction resistance value changes in accordance with a cosine of relative angle in the magnetization directions of the first and second ferromagnetic layers. Therefore, the junction resistance value takes the minimum value when the magnetization directions of the first and second ferromagnetic layers are parallel. On the other hand, the junction resistance value takes when the maximum value when the magnetization directions are anti-parallel. This calls tunneling magnetoresistive (TMR) effect. In this case, according to the TMR effect, a change of the junction resistance value exceeds 70% in room temperature.
In general, in order to write data in a TMR element, write current flows through a write line provided in the vicinity of the TMR element to generate a magnetic field generated from the write line. Then, the magnetic field thus generated is used. In this case, there is a need of providing the write line for generating magnetic field; for this reason, the MRAM size increases.
On the other hand, in order to read data from the TMR element, a switching element is serial-connected to the TMR element, and only switching element connected to a selected read word line is turned on to make a current path. As a result, current flows in the selected TMR element only; therefore, data of the TMR element is read. However, one switch element exists in each cell, and thereby, it is apparent that the cell area increases.
Moreover, an MRAM capable of improving memory capacity has been disclosed as this kind of related technique (see JPN. PAT. APPLN. KOKAI Publication No. 2004-213744).